A gas diffusion electrode easily supplies a gas as a reaction material to the surface of the electrode and has been developed essentially for alkali phosphate type fuel cells, etc., [see; H. Wendt (Elsevier), Electrochemical Hydrogen Technologies, pages 373 et seq.]. Recently, in particular, solid polymeric electrolyte type fuel cells have been actively investigated again and an output of larger than 1 A/dm.sup.2 becomes possible [see, E. A. Ticianelli et al, J. Electroanal. Chem., 251, 275(1988)].
On the other hand, there has been recent investigation of these gas diffusion electrodes for industrial electrolyses. For example, in the production apparatus for hydrogen peroxide on site, the operation is carried out using a water repellent porous cathode for carrying out the oxygen reduction reaction, as described in D. Pletcher, et al., Industrial Electrochemistry. (2nd Edition), pages 279 et seq., published by Chapman & Hall. Also, in alkali production and recovery, the oxygen generation at an anode as a counter electrode reaction, the hydrogen oxidation at an anode in place of the hydrogen generation at a cathode [J. Joerissen et al., J. Applied Electrochem., 21, pages 869.about.(1991)], or the oxygen reduction at a cathode [Miura, et al., J. of the Chemical Society of Japan, 732(1982)] is carried out using a gas diffusion electrode. As a result, the electric power consumed can be reduced. Furthermore, in recovery processes such as the recovery of zinc, etc., and zinc plating, good results are obtained by using a hydrogen anode as a counter electrode [Denki Kagaku oyobi Kogyo Buturikagaku (Electrochemistry and Industrial Physical Chemistry), 56, pages 653 et seq. (1988)].
When a conventional gas diffusion electrode for a fuel cell is used as the gas diffusion electrode in these industrial electrolyses, since the composition of the solution is not simple, unlike the case of a fuel cell, there is the problem that the life of the gas diffusion electrode is liable to be influenced.
A conventional gas diffusion electrode generally has three layers, i.e., a uniform water repellent layer for completely separating a gas from a liquid, an electrically conductive porous layer (metal mesh) for supplying an electric current, and a fine reaction layer having a catalyst. However, when the gas diffusion electrode is used as an oxygen cathode for the electrolysis of sodium chloride, a chlorate ion which is an oxidation product formed at the anode or a hydrogen peroxide ion formed as an intermediate seed by the cathodic reaction chemically acts to the catalyst-carrying powder and/or the water repellent material to separate the foregoing three layers from each other. As a result, the gas-liquid separation ability is sometimes lowered, increasing the electrolytic voltage or causing hydrogen generating reaction.
Also, in this case, if a carbon dioxide gas is intermixed in the supplied electrolyte or gas, it sometimes happens that the carbon dioxide reacts with an alkali to form a carbonate, which deposits as precipitates to clogg the electrode.